On Thursday, September 30, at 5 pm Moscow time, the IdenTrust DST Root CA X3 certificate issued by the Let’s Encrypt center expired.
Because of this, owners of smartphones and computers based on outdated operating systems will face difficulties accessing many Internet sites that use the HTTPS protocol to encrypt the communication channel between the device and the Internet resource.
Instead of the requested page, they will see a warning that the connection to the site is not secure, and an offer to return to a secure resource.
The problem, according to experts, affected the owners of smartphones on Android 7.1 and earlier, iOS 9 and earlier, Windows XP SP2 and a number of other devices. The correct operation of sites is possible when using Firefox 50 and newer – this browser uses its own certificate store. In addition, users are advised to update their devices, if possible, to the most current OS versions.